Abstract:

A motor-driving-circuit comprising: a first to-fourth-transistors; a
drive-control-circuit to control a energization-state of a motor coil so
as to be a driving-state where either one group of a groups of the
first-and-fourth-transistors and the second-and-third-transistors is on
and the other group is off, or so as to be a regeneration-state where the
first-and-third-transistors are off and the second-and-fourth-transistors
are on; a set-current-detection-circuit; an
overcurrent-detection-circuit; and an overcurrent-protection-circuit to
output a regeneration-instruction-signal for shifting the
energization-state to the regeneration-state if an overcurrent-state does
not occur and output a drive-stop-signal for stopping driving the coil if
the overcurrent-state occurs, when a current amount flowing through the
coil has reached a set-level in the driving-state, the
drive-control-circuit shifting the energization-state to the
regeneration-state to be maintained for a predetermined time period and
thereafter returning the energization-state to the driving-state when the
regeneration-instruction-signal is output, and turning off the
first-to-fourth-transistors when the drive-stop-signal is output.

Claims:

1. A motor driving circuit comprising:a first transistor on a power source
side and a second transistor on a ground side connected in series;a third
transistor on the power source side and a fourth transistor on the ground
side connected in series;a drive control circuit configured to control a
energization state of a motor coil so as to be a driving state where
either one group of a group of the first and fourth transistors and a
group of the second and third transistors is on and the other group is
off, or so as to be a regeneration state where the first and third
transistors are off and the second and fourth transistors are on, the
motor coil connected to a connection point of the first and second
transistors and a connection point of the third and fourth transistors;a
set current detection circuit configured to detect whether an amount of
current flowing through the motor coil has reached a set level;an
overcurrent detection circuit configured to detect an overcurrent state
where an amount of current flowing through any of the first to fourth
transistors is over a predetermined amount of current; andan overcurrent
protection circuit configured to output a regeneration instruction signal
for shifting the energization state to the regeneration state in a case
where the overcurrent state does not occur and output a drive stop signal
for stopping driving the motor coil in a case where the overcurrent state
occurs, when the amount of current flowing through the motor coil has
reached the set level in the driving state,the drive control circuit
shifting the energization state to the regeneration state to be
maintained for a predetermined time period and thereafter returning the
energization state to the driving state when the regeneration instruction
signal is output, and turning off the first to fourth transistors when
the drive stop signal is output.

2. The motor driving circuit of claim 1, whereinthe overcurrent protection
circuit outputs the drive stop signal when the overcurrent state has been
maintained for a predetermined time period.

3. The motor driving circuit of claim 1, whereinthe overcurrent protection
circuit includes:a minimum time count circuit configured to count to
measure a minimum time period from a start of the driving state to a
shift to the regeneration state; anda control signal output circuit
configured to output the regeneration instruction signal or the drive
stop signal based on detection results of the set current detection
circuit and the overcurrent detection circuit, after the minimum time
period has been measured by counting.

Description:

CROSS-REFERENCE TO RELATED APPLICATION

[0001]This application claims the benefit of priority to Japanese Patent
Application No. 2009-3940, filed Jan. 9, 2009, of which full contents are
incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002]1. Field of the Invention

[0003]The present invention relates to a motor driving circuit.

[0004]2. Description of the Related Art

[0005]Some motor driving circuits may keep the amounts of currents flowing
through motor coils at set levels by controlling on and off of
transistors connected to the motor coils (Japanese Patent Application
Laid-Open Publication No. 2005-184897). For example, in a motor driving
circuit shown in FIG. 5, an energization state of a motor coil M
connected between terminals T1 and T2 is controlled by on and off of
N-channel MOSFETs 110 to 113 making up an H-bridge. For example, in a
drive control circuit 120, the N-channel MOSFETs 110 and 113 are turned
on and the N-channel MOSFETs 111 and 112 are turned off, so that the
circuit passes the current through a path of the N-channel MOSFET 110,
the motor coil M, and the N-channel MOSFET 113, to drive the motor
(driving state). The amount of the current flowing through the motor coil
M is detected by a resistor R connected via a terminal T3 and when the
amount of the current flowing through the motor coil M reaches the set
level, the drive control circuit 120 turns off the N-channel MOSFET 110
and turns on the N-channel MOSFET 111. As a result, the current, which
the motor coil M tries to continue passing, is regenerated by a loop of
the N-channel MOSFET 111, the motor coil M, and the N-channel MOSFET 113,
and decreases gradually (regeneration state). As such, the drive control
circuit 120 is capable of maintaining the amount of the current flowing
through the motor coil M at the set level by repeating the driving state
and the regeneration state.

[0006]Incidentally, in the motor driving circuit, a load may be
short-circuited due to aged deterioration of the motor, for example. In
the motor driving circuit shown in FIG. 5, if the load is
short-circuited, an overcurrent occurs in a case where the energization
state of the motor coil M is the driving state, and if the overcurrent is
over the set level of the current flowing through the motor coil M, the
drive control circuit 120 changes the energization state of the motor
coil M to the regeneration state. Then, after elapse of a predetermined
time, the drive control circuit 120 changes the energization state of the
motor coil M to the driving state, and the driving state and the
regeneration state are repeated despite the load is short-circuited.
Since the motor driving circuit is generally provided with an overheat
protection function, circuit operation stops before causing circuit
failure even if the driving state and the regeneration state are repeated
in a state where the load is short-circuited. It is desirable, however,
to detect a short circuit of the load and protect the circuit before it
becomes in such an overheated state.

SUMMARY OF THE INVENTION

[0007]A motor driving circuit according to an aspect of the present
invention, comprises: a first transistor on a power source side and a
second transistor on a ground side connected in series; a third
transistor on the power source side and a fourth transistor on the ground
side connected in series; a drive control circuit configured to control a
energization state of a motor coil so as to be a driving state where
either one group of a group of the first and fourth transistors and a
group of the second and third transistors is on and the other group is
off, or so as to be a regeneration state where the first and third
transistors are off and the second and fourth transistors are on, the
motor coil connected to a connection point of the first and second
transistors and a connection point of the third and fourth transistors; a
set current detection circuit configured to detect whether an amount of
current flowing through the motor coil has reached a set level; an
overcurrent detection circuit configured to detect an overcurrent state
where an amount of current flowing through any of the first to fourth
transistors is over a predetermined amount of current; and an overcurrent
protection circuit configured to output a regeneration instruction signal
for shifting the energization state to the regeneration state in a case
where the overcurrent state does not occur and output a drive stop signal
for stopping driving the motor coil in a case where the overcurrent state
occurs, when the amount of current flowing through the motor coil has
reached the set level in the driving state, the drive control circuit
shifting the energization state to the regeneration state to be
maintained for a predetermined time period and thereafter returning the
energization state to the driving state when the regeneration instruction
signal is output, and turning off the first to fourth transistors when
the drive stop signal is output.

[0008]Other features of the present invention will become apparent from
descriptions of this specification and of the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009]For more thorough understanding of the present invention and
advantages thereof, the following description should be read in
conjunction with the accompanying drawings, in which:

[0010]FIG. 1 is a diagram of a configuration of a motor driving circuit
according to an embodiment of the present invention;

[0011]FIG. 2 is a timing chart of one example of an operation when a load
is short-circuited;

[0012]FIG. 3 is a timing chart of one example of an operation when a short
circuit to a high voltage point occurs;

[0013]FIG. 4 is a timing chart of one example of an operation when a short
circuit to ground occurs; and

[0014]FIG. 5 is a diagram of a configuration example of a general motor
driving circuit.

DETAILED DESCRIPTION OF THE INVENTION

[0015]At least the following details will become apparent from
descriptions of this specification and of the accompanying drawings. FIG.
1 is a diagram of a configuration of a motor driving circuit 10 according
to an embodiment of the present invention. The motor driving circuit 10
includes N-channel MOSFETs 20 to 23, a drive control circuit 30,
comparators 32 to 36, reference sources 40 to 42, NAND circuits 45 though
52, an AND circuit 54, NOR circuits 56 and 57, a NOT circuit 58, counters
60 and 61, and a SR flip-flop 63.

[0016]The N-channel MOSFETs 20 to 23 make up an H-bridge circuit, and a
motor coil M is connected, via terminals T1 and T2, between a connection
point of the N-channel MOSFET 20 (first transistor) and the N-channel
MOSFET 21 (second transistor) and a connection point of the N-channel
MOSFET 22 (third transistor) and the N-channel MOSFET 23 (fourth
transistor). The motor coil M is a DC motor coil, for example, and
current flows through the motor coil M in a direction from the terminal
T1 to the terminal T2 so as to rotate a motor in a positive direction
(positive rotation) and the current flows through the motor coil M in a
direction from the terminal T2 to the terminal T1 so as to rotate the
motor in a reverse direction (reverse rotation).

[0017]The drive control circuit 30 controls on and off of the N-channel
MOSFETs 20 to 23 so that the amount of the current flowing through the
motor coil M reaches a set level, according to the direction of the motor
rotation. For example, in the case of the positive rotation, the drive
control circuit 30 firstly turns on the N-channel MOSFETs 20 and 23 and
turns off the N-channel MOSFETs 21 and 22. Thus, the current flows
through a path of the N-channel MOSFET 20, the motor coil M, and the
N-channel MOSFET 23. A state in which the current flows through this path
is referred to as a driving state. When the amount of the current flowing
through the motor coil M reaches a set level, the drive control circuit
30 turns off the N-channel MOSFET 20 and turns on the N-channel MOSFET
21. Thus, the current flowing through the motor coil M is regenerated in
a loop of the N-channel MOSFET 21, the motor coil M, and the N-channel
MOSFET 23. A state in which the current flows through this path is
referred to as a regeneration state. In the case of the reverse rotation,
the current flows through the path of the N-channel MOSFET 22, the motor
coil M, and the N-channel MOSFET 21 in the driving state, and the current
flows in the loop of the N-channel MOSFET 23, the motor coil M, and the
N-channel MOSFET 21 in the regeneration state. Furthermore, when
detecting overcurrent caused by a short circuit to a high voltage point,
a short circuit to ground, or a short circuit of a load, the drive
control circuit 30 turns off all of the N-channel MOSFETs 20 to 23.

[0018]The comparator 32 is a circuit for detecting whether the amount of
the current flowing through the motor coil M has reached the set level
when the motor coil M is in the driving state. Specifically, the
comparator 32 outputs a comparison result of a voltage Vrf generated by
the current flowing through a resistor R connected via the terminal T3
and a reference voltage Vref1 according to the set level output from the
reference source 40.

[0019]The comparator 33 and the NAND circuit 45 make up an overcurrent
detection circuit for detecting whether the current flowing through the
N-channel MOSFET 20 is the overcurrent. In an embodiment according to the
present invention, a voltage Vm-Vref2 that is lower by a reference
voltage Vref2 of the reference source 41 than the power source Vm is
applied to a positive input terminal of the comparator 33. A negative
input terminal of the comparator 33 is connected to the source of the
N-channel MOSFET 20. Therefore, in a state where a signal N1 goes high
and the N-channel MOSFET 20 is turned on, if the overcurrent occurs in
the N-channel MOSFET 20 due to the short circuit of the terminal T1 to
the ground or occurrence of the short circuit of the load, for example, a
voltage drop occurs in the N-channel MOSFET 20 becomes greater than
Vref2, the output of the comparator 33 goes high, and the output of the
NAND circuit 45 goes low. Similarly, the comparator 34 and the NAND
circuit 46 make up an overcurrent detection circuit for detecting whether
the current flowing through the N-channel MOSFET 22 is the overcurrent.

[0020]The comparator 35 and the NAND circuit 47 make up an overcurrent
detection circuit for detecting whether the current flowing through the
N-channel MOSFET 21 is not overcurrent. In an embodiment according to the
present invention, the positive input terminal of the comparator 35 is
connected to the drain of the N-channel MOSFET 21 and the negative input
terminal of the comparator 35 is applied with a voltage which is higher
by a reference voltage Vref3 of the reference source 42 than the voltage
of the source of the N-channel MOSFET 21. Therefore, in a state where a
signal N2 goes high and the N-channel MOSFET 21 is turned on, if the
overcurrent occurs in the N-channel MOSFET 21 due to the short-circuit of
the terminal T1 to a high voltage point, for example, the voltage drop
occurs in the N-channel MOSFET 21 becomes greater than Vref3, the output
of the comparator 35 goes high, and the output of the NAND circuit 47
goes low. Similarly, the comparator 36 and the NAND circuit 48 make up an
overcurrent detection circuit for detecting whether the current flowing
through the N-channel MOSFET 23 is the overcurrent.

[0021]The output signals of the NAND circuits 45 to 48 are input to the
AND circuit 54. Therefore, if the overcurrent occurs in any of the
N-channel MOSFETs 20 to 23, then any of the outputs of the NAND circuits
45 to 48 goes low so that the output of the AND circuit 54 goes low.

[0022]To the NAND circuit 49, the signal N1 to be input to the gate of the
N-channel MOSFET 20 and a signal for instructing the positive rotation or
reverse rotation, which is input from an input terminal IN1, are input.
To the NAND circuit 50, the signal N3 to be input to the gate of the
N-channel MOSFET 22 and a signal obtained by inverting by the NOT circuit
58 the signal input from an input terminal IN1 are input. In an
embodiment according to the present invention, the signal input from the
input terminal IN1 goes high in the case of the positive rotation and
goes low in the case of the reverse rotation. Therefore, in the case of
the positive rotation, the output of the N-channel MOSFET 50 is always
high and the output of the N-channel MOSFET 49 is low only during a time
period in which the signal N1 is high. Similarly, in the case of the
reverse rotation, the output of the N-channel MOSFET 49 is always high
and the output of the N-channel MOSFET 50 is low only during a time
period in which the signal N3 is high. Since the output signals of the
NAND circuits 49 and 50 are input to the NAND circuit 51, the output of
the NAND circuit 51 is high when the energization state of the motor coil
M is the driving state, in either case of the positive rotation or the
reverse rotation.

[0023]The counter 60 (minimum time count circuit) is a circuit for
counting the minimum time of a time during which the energization state
of the motor coil M is the driving state. In an embodiment of the present
invention, when the energization state of the motor coil M becomes the
driving state, the output of the NAND circuit 51 goes high. Therefore,
the counter 60 starts counting when the output of the NAND circuit 51
goes high, and changes the level of the output signal to the high level
when a count value reaches a value corresponding to the minimum time. The
count value of the counter 60 is reset when the output of the NAND
circuit 51 goes low.

[0024]The counter 61 is a circuit for counting a mask time from a time
when the overcurrent is detected until a time when a state is shifted to
a protective state. In an embodiment of the present invention, the output
signal of the AND circuit 54 and the output signal from an output
terminal Q of the SR flip-flop 63 are input to the NOR circuit 56, and
when both of these two signals go low, the output of the NOR circuit 56
goes high. The counter 61 starts counting when the output of the NOR
circuit 56 goes high and changes the level of its output signal to the
low level when a count value reaches a value corresponding to the mask
time. The count value of the counter 61 is reset when the output of the
NOR circuit 56 goes low before the count value reaches the value
corresponding to the mask time. When the output signal of the counter 61
goes low, the drive control circuit 30 determines the presence of the
overcurrent state and turns off all of the N-channel MOSFETs 20 to 23.
Here, the low-level signal output from the counter 61 is one example of a
drive stop signal according to the present invention.

[0025]In the SR flip-flop 63, the output signal of the counter 61 is input
to the inverting set terminal /S thereof and the signal input from the
input terminal IN2 is input to its inverting reset terminal /R thereof.
Therefore, when the signal input to the inverting set terminal /S goes
low, the signal output from the output terminal Q goes high and the
signal output from the inverting output terminal /Q goes low, and when
the signal input to the inverting reset terminal /R goes low, the signal
output from the output terminal Q goes low and the signal output from the
inverting output terminal /Q goes high. The signal input from the input
terminal IN2 goes low at the time of start-up of the motor driving
circuit 10 and thereafter maintains the high level. Therefore, the
signals output from the output terminal Q and the inverting output
terminal /Q of the SR flip-flop 63 are low and high, respectively, at the
initial state. Thereafter, when the signal output from the counter 61
goes low, the signals output from the output terminal Q and the inverting
output terminal /Q of the SR flip-flop 63 go high and low, respectively.

[0026]The output signal of the counter 60, the output signal of the AND
circuit 54, and the signal output from the inverting output terminal /Q
of the SR flip-flop 63 are input to the NAND circuit 52. Therefore, only
when all of these three signals are high, the output signal of the NAND
circuit 52 goes low. The signal output from the NAND circuit 52 and the
signal output from the comparator 32 are input the NOR circuit 57.
Therefore, only when both of these two signals are low, the signal output
from the NOR circuit 57 goes high. When the signal output from the NOR
circuit 57 goes high in a case where the energization state of the motor
coil M is the driving state, the drive control circuit 30 changes the
energization state to the regeneration state. Here, the high-level signal
output from the NOR circuit 57 is one example of a regeneration
instruction signal according to the present invention.

[0027]The circuit including the NAND circuits 49 to 52, the NOR circuits
56 and 57, the NOT circuit 58, the counters 61 and 62, and the SR
flip-flop 63 correspond to one example of an overcurrent protection
circuit according to the present invention.

[0028]FIG. 2 is a timing chart of one example of an operation when the
load is short-circuited. It is assumed that the short circuit of the load
does not occur in the initial state. At the beginning, all of the signals
N1 to N4 input to the gates of the N-channel MOSFETs 20 to 23 are low and
the N-channel MOSFETs 20 to 23 are off.

[0029]Thereafter, at a time T1, when the signals N1 and N4 go high, the
energization state of the motor coil M is changed to the driving state
and the amount of the current flowing though the motor coil M increases.
When the signal N1 goes high, the counter 60 starts counting; and at a
time T2, when a count value reaches a value corresponding to the minimum
time of the driving state at a time T2, the signal B output from the
counter 60 goes high. At this time, since the overcurrent does not occur,
the signal A output from the AND circuit 54 is high, and since the SR
flip-flop 63 is in the initial reset state, the signal D output from the
inverting output terminal /Q is also high. Therefore, all of the signals
A, B, and D input to the NAND circuit 52 are high and the signal E output
from the NAND circuit 52 is changed to the low level.

[0030]Thereafter, the amount of the current flowing through the motor coil
M continues to increase and at a time T3, when it reaches the set level
set by the power source 40, the signal F output from the comparator 32 is
changed to the low level. At this time, since the signal E is also low,
both of the signals E and F input to the NOR circuit 57 are low and the
signal G output from the NOR circuit 57 is changed to the high level.

[0031]When the signal G goes high, the drive control circuit 30 determines
that the amount of the current flowing through the motor coil M has
reached the set level, and at a time T4, allows the signal N1 to be
changed to the low level and the signal N2 to be changed the high level,
and thus, the energization state of the motor coil M is changed to the
regeneration state. Due to the signal N1 being changed to the low level,
the counter 60 is reset and the signal B is changed to the low level. Due
to the signal B being changed to the low level, the signal E goes high
and the signal G goes low.

[0032]After elapse of a predetermined time of the regeneration state, the
drive control circuit 30 allows the signal N1 to be changed to the high
level and the signal N2 to be changed to the low level at a time T5.
Thus, the energization state of the motor coil M is changed again to the
driving state. At this time, if it is assumed that the short circuit of
the load occurs, the amount of the current flowing through the motor coil
M rapidly increases. At a time T6, when the amount of the current flowing
through the motor coil M reaches the set level, the signal F is changed
to the low level. Furthermore, the short circuit of the load causes the
overcurrent in the N-channel MOSFET 20 or the N-channel MOSFET 23, and
thus the signal A is changed to the low level at time T7.

[0033]When the signal N1 goes high, the counter 60 starts counting and the
signal B is changed to the high level at a time T8. At this time, out of
the signals A, B, and D input to the NAND circuit 52, the signals B and D
are high, however, the signal A is low due to the occurrence of the
overcurrent. Therefore, the signal E remains high and the signal G
remains low. As a result, although the amount of the current flowing
through the motor coil M has reached the set level, the signal G remains
low, and thus, the drive control circuit 30 keeps the energization state
of the motor coil M in the driving state.

[0034]When the signal A goes low, the signal output from the NOR circuit
56 goes high and the counter 61 starts counting. Thereafter, at a time
T9, when the count value of the counter 61 reaches the count value
corresponding to the mask time, the signal C is changed to the low level.
When the signal C goes low, the drive control circuit 30 determines that
the signal A is low because of the occurrence of the overcurrent not
because of the effect of the noises, etc., and allows all of the signals
N1 to N4 to be changed to the low level. As a result, the motor coil M
stops driving and the overcurrent state is eliminated.

[0035]FIG. 3 is a timing chart of one example of an operation when the
short circuit to the high voltage point occurs. Here, it is assumed that
the terminal T1 is short-circuited to the high voltage point. In the
initial state, all of the signals N1 to N4 are low and the drive control
circuit 30 allows the signals N1 and N4 to be changed to the high level
at a time T11. Thus, the energization state of the motor coil M is
changed to the driving state. As in the case of FIG. 2, the signal B goes
high and the signal E goes low at a time T12 and the signal F goes low
and the signal G goes high at a time T13.

[0036]When the signal G goes high, the drive control circuit 30 allows the
signal N1 to be changed to the low level and the signal N2 to the high
level at a time T14, as in the case of FIG. 2. As a result, the N-channel
MOSFET 21 is turned on, however, since the terminal T1 is short-circuited
to the high voltage point, the overcurrent occurs in the N-channel MOSFET
21. Therefore, the signal F goes low at a time T15 and the signal A goes
low at a time T16. After elapse of the mask time from the time T16, the
signal C is changed to the low level at a time T17. As at result, the
drive control circuit 30 allows the signals N1 to N4 to be changed to the
low level and the overcurrent state is eliminated.

[0037]FIG. 4 is a timing chart of one example of an operation when the
short circuit to the ground occurs. Here, it is assumed that the terminal
T1 is short-circuited to the ground. In the initial state, all of the
signals N1 to N4 are low, and at a time T21, the drive control circuit 30
allows the signals N1 and N4 to be changed to the high level. As a
result, the N-channel MOSFET 20 is turned on, however, since the terminal
T1 is short-circuited to the ground, the overcurrent occurs in the
N-channel MOSFET 20. At this time, the signal F remains high since no
current flows through the resistor R, however, the signal A is changed to
the low level at a time T22 since the overcurrent occurs in the N-channel
MOSFET 20.

[0038]Thereafter, as in the case of FIG. 2, the signal B is changed to the
high level and the signal E is changed to the low level at a time 23.
Then, when the mask time has passed since the signal A went low, the
signal C is changed to the low level at a time T24. As a result, the
drive control circuit 30 allows all of the signals N1 to N4 to be changed
to the low level and the overcurrent state is eliminated.

[0039]As above, in the motor driving circuit 10 according to an embodiment
of the present invention, when the amount of the current flowing through
the motor coil M has reached the set level, it is shifted to the
regeneration state in the case where the overcurrent does not occur, and
it is not changed to the regeneration state but the overcurrent
protection function is performed in the case where the overcurrent
occurs. Therefore, when the load is short-circuited, there is no
repetition of the driving state and the regeneration state, and thus
safety when the load is short-circuited may be improved. In the motor
driving circuit 10, the overcurrent protection function is performed not
only in the case of the short circuit of the load but also in the case of
the short circuit to the high voltage point and the short circuit to the
ground.

[0040]In the motor driving circuit 10, the mask time of the overcurrent is
set by the counter 61. Therefore, it becomes possible to control stop of
the drive of the motor coil M, when noise is caused in the signal A, for
example.

[0041]In the motor driving circuit 10, the minimum time in the driving
state is set by the counter 60, and even in such a configuration, the
overcurrent protection function may appropriately be performed in any
case of the short circuit of the load, the short circuit to the high
voltage point, or the short circuit to the ground.

[0042]The above embodiments of the present invention are simply for
facilitating the understanding of the present invention and are not in
any way to be construed as limiting the present invention. The present
invention may variously be changed or altered without departing from its
spirit and encompass equivalents thereof.